Re: [libvirt] [PATCH] Revert "virthread: Introduce virRWLockInitPreferWriter"

[Daniel P. Berrange]

On Tue, Jul 25, 2017 at 10:43:50AM +0200, Michal Privoznik wrote:
> This reverts commit 328bd24443d2a345a5832ee48ebba0208f8036ea.
> 
> As it turns out, this is not portable and very Linux & glibc
> specific. Worse, this may lead to not starving writers on Linux
> but everywhere else. Revert this and if the starvation occurs
> resolve it.
> 
> Signed-off-by: Michal Privoznik 

Reviewed-by: Daniel P. Berrange 



Regards,
Daniel
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[libvirt] [PATCH] Revert "virthread: Introduce virRWLockInitPreferWriter"

[Michal Privoznik]

This reverts commit 328bd24443d2a345a5832ee48ebba0208f8036ea.

As it turns out, this is not portable and very Linux & glibc
specific. Worse, this may lead to not starving writers on Linux
but everywhere else. Revert this and if the starvation occurs
resolve it.

Signed-off-by: Michal Privoznik 
---
 src/libvirt_private.syms |  1 -
 src/util/virobject.c |  2 +-
 src/util/virthread.c | 35 ---
 src/util/virthread.h |  1 -
 4 files changed, 1 insertion(+), 38 deletions(-)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 3cc6f4c6e..d98417678 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -2733,7 +2733,6 @@ virMutexUnlock;
 virOnce;
 virRWLockDestroy;
 virRWLockInit;
-virRWLockInitPreferWriter;
 virRWLockRead;
 virRWLockUnlock;
 virRWLockWrite;
diff --git a/src/util/virobject.c b/src/util/virobject.c
index 4236abfef..b1bb378b4 100644
--- a/src/util/virobject.c
+++ b/src/util/virobject.c
@@ -275,7 +275,7 @@ virObjectRWLockableNew(virClassPtr klass)
 if (!(obj = virObjectNew(klass)))
 return NULL;
 
-if (virRWLockInitPreferWriter(>lock) < 0) {
+if (virRWLockInit(>lock) < 0) {
 virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
_("Unable to initialize RW lock"));
 virObjectUnref(obj);
diff --git a/src/util/virthread.c b/src/util/virthread.c
index a8dd72f8b..6c495158f 100644
--- a/src/util/virthread.c
+++ b/src/util/virthread.c
@@ -95,15 +95,6 @@ void virMutexUnlock(virMutexPtr m)
 }
 
 
-/**
- * virRWLockInit:
- * @m: rwlock to init
- *
- * Initializes RW lock using pthread default attributes (which
- * is PTHREAD_RWLOCK_PREFER_READER_NP).
- *
- * Returns 0 on success, -1 otherwise.
- */
 int virRWLockInit(virRWLockPtr m)
 {
 int ret;
@@ -115,32 +106,6 @@ int virRWLockInit(virRWLockPtr m)
 return 0;
 }
 
-
-/**
- * virRWLockInitPreferWriter:
- * @m: rwlock to init
- *
- * Initializes RW lock which prefers writers over readers.
- *
- * Returns 0 on success, -1 otherwise.
- */
-int virRWLockInitPreferWriter(virRWLockPtr m)
-{
-int ret;
-pthread_rwlockattr_t attr;
-
-pthread_rwlockattr_init();
-pthread_rwlockattr_setkind_np(, 
PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP);
-ret = pthread_rwlock_init(>lock, );
-pthread_rwlockattr_destroy();
-if (ret != 0) {
-errno = ret;
-return -1;
-}
-return 0;
-}
-
-
 void virRWLockDestroy(virRWLockPtr m)
 {
 pthread_rwlock_destroy(>lock);
diff --git a/src/util/virthread.h b/src/util/virthread.h
index 18b785af2..e466d9bf0 100644
--- a/src/util/virthread.h
+++ b/src/util/virthread.h
@@ -136,7 +136,6 @@ void virMutexUnlock(virMutexPtr m);
 
 
 int virRWLockInit(virRWLockPtr m) ATTRIBUTE_RETURN_CHECK;
-int virRWLockInitPreferWriter(virRWLockPtr m) ATTRIBUTE_RETURN_CHECK;
 void virRWLockDestroy(virRWLockPtr m);
 
 void virRWLockRead(virRWLockPtr m);
-- 
2.13.0

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